string theory
The study of string theory over the past few years has, if nothing else, revealed a profound connection between gravity and gauge theories. In its most concrete form, this correspondence has been enunciated in Maldacena's conjecture that superstring theory on a certain negatively curved ten dimensional space is dual to a supersymmetric gauge theory living on its boundary. From this point of view, there appears to be a more practical application of string theory: the understanding of gauge theories with the primary goal to be able to make quantitative predictions about ordinary QCD.
AdS/CFT correspondence
With this goal in mind, there remains much to be learnt about the gauge/gravity duality. In particular, built into the AdS/CFT correspondence is a dictionary that faithfully maps string states on the gravity side to certain gauge invariant operators in the field theory. Clearly then, the better that the dictionary is understood, the closer we will be to proving the duality. Our work in the string theory subgroup has focussed on understanding and applying the gauge theory/gravity duality to various contemporary problems in high energy physics.
string cosmology
On the other hand, one of the most facinating testing grounds for string theory and string theory inspired ideas is in the physics of the early universe. From the initial singularity to the current acceleration of the universe, cosmology offers a wonderful - indeed possibly the only viable - laboratory to test ideas from string theory. However, cosmological questions remain among the most difficult to ask within string theory primarily because of our lack of understanding of the degrees of freedom afforded to us. So, for example, time dependent singularities like the Big-Bang are difficult to understand precisely because we have no control over which are the relevant degrees of freedom near these spacetime points. It is an exciting prospect that the gauge theory/gravity correspondence will provide insight into the resolution of this problem.
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